1. Field of the Invention
The invention relates to a multi-band antenna with a broadband function and, in particular, to a multi-band antenna based upon a planar inverted-F antenna (PIFA) and having two conductive arms disposed at both ends of a ground, wherein the radiation plates of the conductive arms extend toward each other.
2. Description of Related Art
Personal mobile communications have great potential and business opportunities in the wireless communication industry. During their evolution, many systems adopting different techniques and channels have been developed. Therefore, they play important roles in different areas and markets. However, this phenomenon causes troubles and inconvenience for the system suppliers and consumers. One consequential point is that different systems, e.g., GSM900, DCS1800, and PCS1900, use different frequency bands.
For the convenience of users, manufacturers have spent a lot of manpower to develop multi-band mobile phones. Among all difficulties, the antenna is still the key factor in the wireless communications designs. It demands the following requirements.
1. Frequency and bandwidth.
2. Matches between the radiation field patterns and polarization of the antenna.
Compactness and light-weight are the trend in electronic product designs. The same also applies to mobile phones. This affects their antenna designs. The planar inverted-F antenna (PIFA) is thus widely used because its length can be reduced to ¼ wavelength (the length of a usual antenna is ½ wavelength). Therefore, it can greatly reduce the area occupied by the antenna in the electronics. Moreover, the PIFA helps achieving the object of hiding the antenna. The PIFA operated in a single frequency can be found in U.S. Pat. No. 5,764,190. Later on, for the PIFA to be operated in multiple frequencies, radiation metal plates are also formed with L-shaped or U-shaped holes.
Another antenna that achieves multi-band operations is shown in FIG. 1. The antenna includes a first radiating part A, a second radiating part B and a ground C. Both the first radiating part A and the second radiating part B extend from the opposite sides of the ground C. The first radiating part A includes a first conductive plate A1 parallel to the ground C and a first connecting part A2 that is connected between the first conductive plate A1 and the ground C. The radiating part B includes a second conductive plate B1 parallel to the ground C and a second connecting part B2 that is connected between the second conductive plate B1 and the ground C. The first conductive plate A1 and the second conductive plate B1 extend respectively from the first connecting part A2 and the second connecting part B2 toward the same direction.
Although the above-mentioned antenna can be operated in multiple frequency bands, it has the following disadvantages. The first connecting part A2 and the second connecting part B2 are too close to each other, and inconvenient for operations at high frequencies. Moreover, since the first conductive plate A1 and the second conductive plate B1 extend respectively from the first connecting part A2 and the second connecting part B2 toward the same direction, bending the first radiating part A and the second radiating part B is difficult when fabricating the antenna. It is also difficult to connect a feed wire to the first conductive plate A1 by soldering.
The invention thus proposes a design that can greatly enlarge the high frequency band for multi-band operations and simplify the antenna manufacturing as well.